The present invention relates to an improved apparatus for measuring the breathability of a shoe and its level of comfort.
It is known that human perspiration occurs by expelling sweat through the pores of the skin, which are each connected to sweat glands.
The generated sweat is liquid, and once it has made contact with the warm skin it evaporates, removing its own latent heat of evaporation (approximately 580 calories/g at 30° C.).
This fact cools the skin and activates body thermoregulation.
Some systems commonly used to measure the breathability of items of clothing or shoes relate only to the materials that compose them.
These systems allow to obtain data related to breathability defined in milligrams per square centimeter per hour, or in grams per square meter per day.
The basic conditions of the tests are defined for example in the UNI 8429 standard, but they cannot be applied for example to an entire shoe, since they do not provide the necessary conditions such as the presence of multiple layers, the movement of the foot and the different sweat production conditions.
A complex simulation system has also been devised which is based on the measurement of the difference in breathability between a water-resistant but non-breathable article and an article provided with a waterproof and breathable membrane, a system which is therefore partly capable of simulating the generation of vapor by the human foot and therefore of measuring the vapor permeability of a shoe.
This system is disclosed in U.S. Pat. No. 4,918,981, which relates indeed to a method and an apparatus for testing items to be worn, such as for example shoes, gloves, et cetera, that form closed elements for transmitting the vapor generated by perspiration.
The apparatus comprises a thin, flexible and waterproof closed jacket, which is highly vapor-permeable, is inserted in the item to be tested and is filled with water.
The water can be heated in order to simulate the temperature of the body and produce a high concentration of moist vapor inside the item.
The amount of humidity transferred to the environment outside the item being tested and the amount of humidity absorbed and condensed in the item can be measured by means of weight differences on measurements made before, during and after the test period.
Still, the application of this system to shoes does not yield uniform and reliable results, since the actual operating conditions to which the foot is subjected, particularly during walking and/or running, are not simulated, and because the microclimate that occurs inside a shoe during use is not replicated.
Other devices are also known which are capable of producing sweat (vapor) in a known quantity, but their adjustment systems are not precise enough to be self-adjusting and in any case do not replicate the actual heat exchange and vapor exchange phenomena that occur in a foot-shoe system.
An apparatus for measuring the breathability of a shoe has also been devised recently and is disclosed in U.S. Pat. No. 6,487,891; such apparatus comprises, on a supporting footing, a hollow body made of self-supporting material, that reproduces the contour of a foot adapted to support the shoe to be tested.
The body has through holes that are distributed thereon and contains water.
A sock made of waterproof and breathable material (membrane) is arranged so as to enclose the hollow body.
A presser element is provided in order to perform relative movements with the hollow body between a spaced configuration and a configuration in which it is compressed against the sole of the shoe.
The apparatus further comprises means for heating the water in the hollow body to a preset and constant temperature and means for measuring the weight of such hollow body together with everything that is associated therewith and the shoe to be tested.
Such apparatuses, and in particular the last one, which in practice has proved to be qualitatively the best, despite constituting technological steps forward, have been found to suffer drawbacks, including:                difficulty in inserting the shoe        easy rupture of the sock during the test, accordingly causing losses of liquid that alter the results        poor accuracy of the adjustment of the internal temperature, which in any case cannot be diversified according to the various regions of the foot        impossibility to adjust the amount of vapor generated independently of the temperature values        impossibility to determine the corresponding values of internal relative humidity between the shoe and the artificial foot generated after supplying a known amount of water        poor reproducibility of the data (VC<20%), which makes the data scarcely significant and usable        non-reproducibility of the actual physiological phenomenon of perspiration.        
It should also be noted that in any case it is not possible to determine the amount of heat, or more generally the energy dissipated by a shoe-foot system.